1. Field of the Invention
The present invention relates to a control apparatus and a control method for an internal combustion engine that divides the inside of a combustion chamber into a layer of internal EGR gas and a combustible layer to perform stratified combustion.
2. Description of Related Art
Conventionally, as disclosed in Japanese Laid-Open Patent Publication No. 2008-255866, there has been an internal combustion engine that divides the inside of a combustion chamber into a layer of internal EGR gas and a combustible layer to ignite the combustible layer to thereby perform stratified combustion.
In the internal combustion engine, internal EGR gas is introduced into a first intake port located upstream of a first intake valve in an exhaust stroke. Then, in an intake stroke, the internal EGR gas in the first intake port is introduced into a combustion chamber through the first intake valve and fresh air in a second intake port located upstream of a second intake valve is introduced into the combustion chamber to generate a layer of internal EGR gas and a combustible layer in the combustion chamber.
In the meantime, in the conventional technique, the first intake valve provided in the first intake port into which the internal EGR gas is introduced is closed in the middle of the intake stroke. This results in interrupting the introduction of intake air through the first intake port in the middle of the intake stroke. As a result, the gas flow in the combustion chamber is weakened, causing a problem that mixing of fresh air and fuel cannot be promoted sufficiently.
Here, if the gas flow is enhanced, mixing of fresh air and fuel can be promoted. However, when the gas flow is enhanced, fuel is more likely to be mixed into internal EGR gas and the amount of internal EGR gas cannot be increased sufficiently.